STANDING ON THE pier in Old Town Alexandria, surrounded by magnificent sailboats and cabin cruisers, I thought all I needed to be enjoying a day on the river was a captain's hat, deck shoes and -- oh yes -- a boat.

But knowing the closest I'd ever get to a 50-foot boat was at the boat show, I decided to investigate more modest ways to get on the water.

Thinking that small might be the perfect way to go, I left the Potomac River behind and headed to one of the area's many lakes.

Just minutes from Gaithersburg in Seneca Creek State Park is Clopper Lake. As I drove along the winding roads, I caught glimpses of the boathouse and people on the water through the trees. Although man-made, the setting is rustic with the shoreline heavily treed.

This 90-acre lake is home to beavers, largemouth bass, catfish and bluegills. Overlooking the lake is a large boathouse with a snack bar and gift shop. Available for rent are rowboats, canoes, pedal boats and sailboats. For larger groups, there's a pontoon boat. Never really being too proficient in canoeing or sailing, I chose a four-person pedal boat, figuring once I got my sea legs I could move up to rowing.

After 25 minutes of foot exercise, I relinquished command of the pedal boat and hopped aboard the pontoon for a tour of the lake. As we pushed away from the dock, Ranger JoAnn Berisford, our guide for the next hour, told us to be on the lookout for the wildlife on the lake -- Canada geese, ducks, green herons, great blue herons, osprey and bald eagles, which sometimes fly through. On the Saturday evening tours, deer, fox, raccoons and wild turkeys can be seen. And in the water busy beavers often swim by.

I'm seriously thinking about buying deck shoes, a captain's hat and maybe even a fishing pole to use while I'm paddling around the water this summer. And if you go, don't forget to pack suntan lotion and a cool drink -- it's hot out there. ROW THEIR BOAT

The following locations offer boat rentals. Life jackets, which are required, are included in the rental fee unless indicated. VIRGINIA


7315 Ox Rd., Fairfax Station. 323-6600. 218 acres. Open 6 a.m. until dark daily. All-day rowboat rentals $9 plus $1 for life jacket; $4.50 after 4 p.m.


1400 Lake Fairfax Dr., Reston. 471-5414. 30 acres. Open 10 to 8 daily. Pedal boats $3.50 per half-hour.


Fountainhead Regional Park, 10875 Hampton Rd., Fairfax Station. 703/250-9124. 3,000 acres. Open 6 a.m. to 8:45 p.m. daily. All-day flat-bottom rowboat rentals $9 plus $1 for life jacket; you can bring your own electric motor up to 10 horsepower. MARYLAND


Cosca Regional Park, 11000 Thrift Rd., Clinton. 868-1397. 15 acres. Open noon to 7 Tuesday through Sunday. Rowboats and canoes $2.50 per half-hour, pedal boats $3.


Seneca State Park, 11950 Clopper Rd., Gaithersburg. 963-8788. 90 acres. 0pen 8 to sunset daily. Hourly rates: rowboats $3, canoes $4, two-person pedal boats $4, four-person pedal boats $6. Pontoon boat rides cost 75 cents and are at 1:30, 3, 4:30 and 7:45 weekends; reservations required for Saturday evening. Park admission is $4 for Maryland residents, $5 out of state.


Rock Creek Regional Park, 15700 Needwood Lake Circle, Rockville. 948-5053. 74 acres. Open 10 to 6 Tuesday through Friday, 6:30 to 6 weekends and holidays; closed Mondays. Rowboats and canoes $3.68 per hour, pedal boats $3.94 per half-hour.


Black Hill Regional Park, 20930 Lake Ridge Dr., Boyds. 972-6157. 505 acres. Open 10 to 6 weekdays, 6:30 to 6 weekends. Rowboats and canoes $3.50 hourly, $15.50 daily. Pontoon boat rides cost $1 and leave hourly from noon to 6 weekends.


Patuxent River Park, 16000 Croom Airport Rd., Upper Marlboro. 627-6074. Open 8 to 8 daily. Canoes $10 daily; reservations required.


Two miles north of Falls and River roads, on the C&O Canal in Great Falls. 299-9006. Open 9 a.m. weekdays, 6:30 a.m. weekends; return half-hour before dark. Canoes and rowboats $6.65 hourly, $15.45 daily. THE DISTRICT


Canal and Reservoir roads NW. 244-0461. On the Potomac or C&O Canal. Open 9 to 7:30 weekdays, 7:30 to 7:30 weekends, weather permitting. Daily canoe and rowboat rental $13 weekdays, $14 weekends.


3500 K St. 337-9642. On the Potomac. Open 10 to 8 weekdays, 8 to 8 weekends. Rowboats and canoes $15 daily or $10 for 2 hours or less.


Rock Creek Parkway and Virginia Avenue NW. 333-4861. On the Potomac. Open 9 to 5 weekdays, 9 to 6 weekends. Rowboats and canoes are $4.75 hourly, $15 daily; hourly boat rates are shells $10, double shells $15 and Sunfish $10.


15th Street and Maine Avenue SW. 484-0206. Open 10 to 8:30 daily. Pedal boats $7 hourly.

Alice Rindler Shapin last wrote for Weekend about the Baltimore Zoo.